Known force sensors are designed as frequency-analog resonant mechanical sensors. Such known force sensors include a structure that vibrates in resonance. The oscillation frequency of this structure is variable on the basis of an acting force, such as an acceleration or a pressure, to be detected. Due to the external action of the acting force, the structure vibrating in resonance is deflected so that it changes its oscillation frequency. The structure vibrating in resonance is formed by a spring-mass system, where an increase in sensitivity of a force sensor can be achieved by an increase in the seismic mass, a reduction in rigidity of the springs, or a combination of the two measures.
However, a disadvantage of the known force sensor discussed above is that a reduction in the fundamental frequency at which the structure vibrates in resonance occurs, so that there is a negative effect on sensor dynamics. On the other hand, an increase in sensor dimensions is associated with an increase in seismic mass.
German Published Patent Application No. 4,426,163 describes an acceleration sensor where the structure vibrating in resonance is under a mechanical prestress, so that the force sensor is operated near its mechanical instability. This increases the sensor sensitivity of the force sensor by placing an operating point of the sensor closer to the mechanical instability. The distance of the operating point from the mechanical instability is determined by a parameter of the applied mechanical prestress. However, it is a disadvantage here in that it is difficult to accurately set the distance of the operating point from the mechanical instability, e.g., due to geometric tolerances in the layout of the sensor, due to temperature dependences, and due to layer stresses which occur due to the mechanical prestress and are difficult to control. Especially when the force sensor is to be operated near its mechanical instability to increase sensor sensitivity, even the slightest shifts in operating point will lead to great signal variations and thus signal errors.